This invention relates generally to a fuel injection pump of the distribution type, and more particularly to an improved load timer for adjusting the fuel injection timing in accordance with the load of an engine.
Japanese Laid-Open (Kokai) Patent Application No. 119132/82 discloses a fuel injection pump of the distribution type. This fuel injection pump is provided with a housing 2 whose internal space serves as a pump chamber. A drive shaft 6 to which the rotation of an engine is transmitted extends into the housing 2. One end portion of the drive shaft 6 disposed within the pump chamber is connected to one end of a plunger 5 through a coupling so as to rotate the plunger 5 in a manner to allow an axial movement of the plunger 5. The other end of the plunger 5 cooperates with the housing to form a fuel pressurizing chamber 14. The rotational movement of the plunger 5 serves to distribute the fuel in the fuel pressurizing chamber sequentially to a plurality of injection nozzles. Cam mechanisms 7 and 8 for reciprocally moving the plunger 5 axially in response to the rotational movement of the plunger 5 are provided within the pump chamber. When the plunger 5 moves in one direction (that is, at a suction stroke), it draws the fuel into the fuel pressurizing chamber 14, and when the plunger 5 moves in the other direction (that is, at a pumping stroke), it pressurizes the fuel in the fuel pressurizing chamber 14.
A control sleeve 19 is axially slidably mounted on the outer periphery of the plunger 5. A cut-off port 31 in the plunger 5 is closed by the control sleeve 19 during the pumping stroke, and when the cut-off port 31 moves away from the control sleeve 19, the pressurized fuel in the fuel pressurizing chamber 14 escapes to the pump chamber via the cut-off port 31, thus finishing the fuel injection. The position of the control sleeve 19 determines the amount of injectin of the fuel. A lever assembly is pivotally supported within the housing 2. The position of the control sleeve 19 and hence the fuel injection amount are adjusted by this lever assembly. A governor spring 41 for receiving an operating force of an accelerator pedal is accommodated within the housing 2. The governor spring 41 urges the lever assembly to be pivotally moved so as to move the control sleeve 19 in the direction of the pumping stroke of the plunger 5, that is, so as to increase the fuel injection amount. A governor is also received within the housing 2. This governor urges the lever assembly to be pivotatlly moved so as to move the control sleeve 19 in the direction of the suction stroke of the plunger 5, that is, so as to decrease the fuel injection amount. This governor comprises a governor shaft 45 fixedly mounted on the housing 2 and extending into the pump chamber, a governor sleeve 37 axially slidably mounted on the outer periphery of the governor shaft 45, a rotation member 46 mounted on the governor shaft 45 so as to be rotated by the rotation of the drive shaft 6, and fly weights 47 supported on the rotation member 46. Under the infuence of the centrifugal force of the fly weight 47 caused by the rotation of the rotation member 46, the governor sleeve 37 urges the lever assembly to be pivotally moved.
A main timer 39 is provided on the housing 2. The main timer 39 adjusts the above cam mechanisms 7 and 8 in accordance with the pressure in the pump chamber so as to adjust the fuel injection timing. This adjustment is made in such a manner that the higher the pressure in the pump chamber is, the earlier the fuel injection timing is.
The fuel injection pump of the above prior publication is also provided with a load timer which cooperates with the main timer 39 to adjust the fuel injection timing in accordance with the load of the engine. This load timer includes the above-mentioned governor. The load timer further includes a relief hole 49 formed in the governor shaft 45 and extending axially thereof, a first communication passage passing through the peripheral wall of the governor shaft 45 surrounding the relief hole 49, and a second communication passage passing through the peripheral wall of the governor sleeve 37. The first communication passage has a single annular groove 48 formed in the outer peripheral surface of the governor 45, and a port communicating the annular groove 48 with the relied hole 49. The second communication passage is defined by a single control hole 50 of a small cross-sectional area.
The above load timer is of a well-known contruction. In this load timer, when the engine load is low, the governor sleeve 37 is positioned forwardly, and therefore the control hole 50 is in communication with the annular groove 48, so that the pressure in the pump chamber escapes to the relief hole 49. The area of communication between the control hole 50 and the annular groove 48 is equal to the total cross-sectional area of the annular groove 48, and therefore the pressure in the pump chamber is at the minimum level, so that the fuel injection timing determined by the main timer is the latest. As the engine load increases, the governor sleeve 37 is gradually retracted, and therefore the area of communication between the control hole 50 and the annular groove 48 is gradually decreased, so that the pressure in the pump chamber increases, and therefore the fuel injection timing becomes earlier or advanced. When the engine load further increases, so that the governor sleeve 37 retracted, the control hole 50 is closed by the governor shaft 45, and therefore the pressure in the pump chamber is increased, so that the fuel injection timing becomes the earliest.
In the above known load timer, during the idling of the engine immediately after the start of the engine at cold places or high places, the fuel injection timing is late or delayed because of a low engine load, and therefore the engine may be stopped or may produce smoke. To deal with such difficulty, the fuel injection pump of the above prior publication is provided with a solenoid valve 51 for opening and closing the relief hole 49, and a control unit 52 for controlling the solenoid valve 51. The control unit 52 controls the solenoid valve 51 in accordance with information (e.g. the temperature of cooling water for the engine, the atmospheric pressure, the engine load, and so on) inputted thereto, so that the fuel injection timing can be advanced or made earlier even during a low-load operation of the engine. However, the addition of the solenoid valve 51 increases the cost involved.
Japanese Laid-Open Utility Model Application No. 12743/87 also discloses a load timer for a fuel injection pump of the distribution type. As best shown in FIG. 1 of this prior publication, two annular grooves 59 and 60 are formed in an outer periphery of a governor shaft 42, and are spaced from each other axially of the governor shaft 42, the annular grooves 59 and 60 serving as first communication passages. Two annular grooves 57 and 58 are formed in an inner periphery of a governor sleeve 41, and serve as second communication passages. When the engine load is low, the area of communication between the annular grooves 57 and 59 is large, and also the area of communication between the annular grooves 58 and 60 is large. Therefore, the fuel injection timing is late. As the engine load increases, the area of communication between the grooves 57 and 59 and the area of communication between the grooves 58 and 60 are decreased, so that the fuel injection timing is advanced. Then, when the engine load increases to a certain level, the communication between the grooves 57 and 59 is interrupted, and also the communication between the grooves 58 and 60 is interrupted, so that the fuel injection timing becomes the earliest. The pair of annular grooves are formed in each of the governor shaft 42 and the governor sleeve 41, and therefore the rate of increase of the pressure of the pump chamber (the degree of advance of the fuel injection timing) relative to the increase of the engine load (the fuel injection amount) can be twice higher than that obtained with the provision of a single first communication passage and a single second communication passage (see FIG. 2). Also, by changing the width of the annular grooves, a characteristics line, representing the degree of advance of the fuel injection timing relative to the engine load, can have two different gradients, as shown in FIGS. 4 to 6 of this prior publication.
In the load timer of the above Japanese Laid-Open Utility Model Application No. 12743/87, however, the fuel injection timing can not be advanced in a low engine load region. Further, the fuel injection timing can not be delayed in accordance with the increase of the engine load from the low engine load region.